Scaling and point of origin
These commands should help:
"Set Origin"
  here you have several options in Objekt mode to place your origin
"Snap Cursor to Active" + "Median Point Menue": 3D Cursor
  here you can change your origin while beeing in Edit-Mode for 
  scaling from percise points  



Also you should look into the realation between Edit and Objekt mode:
Editmode transformation dont change the Objekt-Mode origin.